RE: pg_upgrade and logical replication

Dear Michael,

> I'd like to propose a check
> for IsBinaryUpgrade into ApplyLauncherRegister() instead as it makes
> no real sense to start apply workers in this context.  That would be
> equivalent to max_logical_replication_workers = 0.

Personally, I prefer to change max_logical_replication_workers. Mainly there are
two reasons:

1. Your approach must be back-patched to older versions which support logical
   replication feature, but the oldest one (PG10) has already been unsupported.
   We should not modify such a branch.
2. Also, "max_logical_replication_workers = 0" approach would be consistent
   with what we are doing now and for upgrade of publisher patch.
   Please see the previous discussion [1].

[1]: https://www.postgresql.org/message-id/CAA4eK1%2BWBphnmvMpjrxceymzuoMuyV2_pMGaJq-zNODiJqAa7Q%40mail.gmail.com

Best Regards,
Hayato Kuroda
FUJITSU LIMITED